The invention relates to a method for deforming a hollow tubular workpiece, wherein the workpiece is clamped down in a clamping device, a first forming tool is placed into contact with the outer surface of the workpiece, said tool is rotated about an axis of rotation relative to the workpiece and one end of the workpiece is deformed by means of said first tool. The invention furthermore relates to a forming machine in accordance with the preamble of claim 7.
Such a method and forming machine are known, for example from European patent application No. EP 0 916 428. Said publication discloses a method and a forming machine, comprising a forming head fitted with a number of rollers, by means of which the diameter of one end of a cylindrical metal element is reduced and moreover bent through an angle.
To this end, the metal cylinder is clamped down and said cylinder and said forming head are rotated relative to each other about an axis of rotation, whereupon said end is deformed by pressing said rollers in radial direction against the outer surface of said cylinder and moving them along said outer surface in a number of cycles, whereby the radial distance between the rollers and the axis of rotation is decreased with each cycle, as a result of which a reduction of the diameter is obtained. Since the axis of rotation is at an angle with the central axis of the metal cylinder, the end of the cylinder is not only reduced as a result of the movement in radial direction of the rollers, but in addition said end will also be positioned at an angle. Due to the use of the aforesaid cycles, the workpiece assumes the shape of the final product step by step.
EP 0 916 426 discloses a comparable method and forming machine, wherein the axis of rotation is eccentrically offset from the central axis of the metal cylinder. Thus a product is obtained wherein the central axis of the deformed portion is likewise offset from the central axis of the undeformed portion of the metal cylinder.
The method and forming machine in hand can be used, for example, in the production of the housings of catalytic converters that form part of the exhaust system of vehicles, such as passenger cars. Such catalytic converters have a diameter which is larger than the diameter of the pipes of the exhaust system of which they form part, and they are preferably positioned close to the engine block in order to reach their operating temperature as quickly as possible after the engine has been started and to maintain that temperature as much as possible. One consequence of this is that, first of all, the diameter of the connections on either side of the catalytic converter housing must be reduced in order to properly connect to the rest of the exhaust system and that in addition they often need to have a complicated shape in order to enable an optimum position with respect to the engine block.
When using the prior art methods and apparatuses for producing workpieces having two deformed ends, such as e.g. the above-described catalytic converter housings the clamped-down workpiece must be detached after one end has been worked and be clamped down anew for working the other end.